1. Field of Invention
This invention relates to a shaft coupling apparatus, and more particularly, to an apparatus for providing a repositionable paddle assembly for varying the relative pitch angle between oppositely disposed paddle blades.
2. Description of Related Art
The sport or activity of kayaking is rapidly growing in popularity as it provides a source of enjoyment/entertainment, rigorous exercise, and a unique connection with nature. One can analogize kayaking to the sport of cycling inasmuch as each involves individual effort, self-motivation, and self-propulsion.
While kayaking has many similarities to cycling, there is a large disparity in the number of individuals who enjoy each activity. Aside from the obvious need for a body of water, the cost and convenience of kayaking is, perhaps, the largest deterrent to involvement in the sport. Fortunately, recent innovations in kayak and kayak paddle design and manufacture have made kayaking more affordable, easier to handle/maneuver, and less cumbersome to transport.
Consequently, there is a constant evolution in kayak paddle design aimed at making kayaking more enjoyable. For example, Aqua-Bound Technology Ltd., one of the largest manufacturer's of kayak paddles and accessories, were one of the first to introduce gas assist injection molded kayak paddles which made paddles, previously one of the most expensive accessories required, much more affordable.
Other advances in the area of kayak design and construction, to which the present invention is directed, relates to reconfiguring twin-bladed paddle assemblies to vary the pitch angle between opposing blades. Paddle blade assemblies are often constructed with a pair of paddle blades mounted at opposite ends of a central handle. While such paddle assemblies facilitate an ergonomically smooth motion i.e., as a paddler passes each paddle blade through the water to either side of a kayak, the paddle blade which rises above the water can produce significant aerodynamic drag especially in windy conditions. That is, when a paddler passes one paddle blade through the water, the opposing blade can, if disposed at a high angle of attack relative to the freestream airflow, produce significant profile drag. Such drag forces are, it will be appreciated, exacerbated by high wind speeds/gusts commonly produced on the water. To counteract such drag forces, it is typical for paddle assemblies to include a center coupling capable of varying the relative pitch angle of the paddle blades. That is, by disposing the blades at a relative pitch angle of, for example, 60 to 90 degrees, the paddle blade in the free stream airflow can be feathered to an angle close to a zero angle of attack. Furthermore, depending upon the direction of the wind relative to the watercraft, other pitch angles may be desired to minimize drag.
U.S. Pat. No. 4,605,378 to Hamilton discloses a repositionable coupling which employs a spring biased pin disposed in telescoping segments of a paddle assembly. The pin, which is connected to one of the paddle segments, seats within an aperture of the other segment. By depressing the spring biased pin, the paddle assemblies may be rotated until the pin is reset into a second aperture, e.g., disposed 90 degrees apart from the first, to change the relative pitch angle of the paddle blades. While this paddle design addresses the difficulties associated with aerodynamic drag, the repositionable coupling has certain design deficiencies. For example, only a limited number of apertures can be employed without impacting the structural integrity of the paddle assembly. Hence, the relative rotational position of the paddle assemblies is limited to several choices, e.g., +/−90 degrees.
Furthermore, after extended use, the coupling can fail or develop “play” due to fretting wear between the pin and aperture. That is, the aperture can become elongated or oval-shaped over time such that the coupled components become loose and prematurely fail.
Yet other prior art coupling arrangements such as that illustrated in U.S. Pat. No. 6,881,111 to Bridge, et al. employ a combination of spring biased pins and a spline for accepting an elongate key. While this coupling design eliminates the structural deficiencies of the Hamilton '378 patent, i.e., by separating the axial and torsional load paths, this arrangement employs a number of moving parts and/or high tolerance connections. As such salt water corrosion of the spring mechanism as well as debris from sand or salt deposits can jam or otherwise render the coupling inoperable.
A need, therefore, exists for a reliable and secure repositionable coupling which enables greater flexibility in terms of paddle blade positioning.